1. Field of the Invention
The present invention relates to an image processing apparatus and method for performing color determination processing.
2. Description of the Related Art
In a conventional image processing apparatus, various techniques are used in order to improve printing speed. For example, technology is known whereby in an image processing apparatus employing an inkjet method in a printing unit, the printing speed of monochrome images is improved by increasing the range that can be printed at once by adopting a greater length for a row of nozzles used for black (Bk) printing than for other rows of nozzles used for color printing.
Also, technology is known whereby using this elongated row of nozzles for Bk printing, printing speed is also improved for text or the like that is unintentionally processed as a color image due to a color shift when reading a color copy (Japanese Patent No. 3762267). According to this technology, image data is divided into unit regions having a predetermined number of lines, features of those unit regions are determined, and the row of nozzles used is switched for each unit region. For a color region that includes a color image, both rows of nozzles for color printing and a longer row of nozzles for Bk printing are used, and for a monochrome region that includes a monochrome image but not a color image, only the longer row of nozzles for Bk printing is used. Thus, high speed printing can be executed.
However, with a conventional technique of printing acceleration employing region determination, the region determination is only performed at pixels constituting a unit region, so there is the problem that for an object spanning a plurality of unit regions, determination results are switched in the midst of the object. For example, with image data as shown in FIG. 5A (where B indicates a black object, and C indicates a color object), according to the conventional technique, as shown in FIG. 5B, the region determination results may sometimes be switched in the midst of objects B4 and B5. In such a case, there are the problems that for a black object, there occurs both a portion in which monochrome is determined and so printing is performed with only Bk ink, and also a portion in which printing is performed with both Bk ink and CL ink, and above and below a border, coloration differs due to different ink being used (a region of color ink and Bk ink versus a region of only Bk ink), and the perception of granularity differs due to a difference in the size of nozzles used.
If the row of nozzles used is switched on a per-object basis, a border does not occur, but in this case it is necessary to determine whether or not an object continues in the vertical direction and/or in the horizontal direction. Therefore, it is necessary to determine attributes in narrowly divided regions, and as a result there is the problem that the processing load increases.